This invention relates to method and apparatus for detecting the presence of a predetermined concentration of one liquid such as water in another liquid such as oil. The oil may, for example, be a hot oil bath which is used for quenching workpieces after the workpieces have been heated in a heat treating furnace. A controlled atmosphere (e.g., a carbon enriched atmosphere) is sometimes maintained in the furnace in order to impart desirable characteristics to the workpieces during the heating process, and such atmosphere can exist above the oil bath.
The oil of a quenching bath is frequently flashed to high temperatures by the hot workpieces thus giving rise to the danger of an explosion resulting from minute amounts of water which, for various reasons, may be present in the oil. As the oil is heated, such water may vaporize and bubble to the surface. The steam bubbles carry with them small quantities of oil vapor which mixes with the atmosphere above the oil surface. The resulting oil vapor atmosphere is very combustible. To preclude the danger of explosion, the heat treating industry has determined that the oil should not contain more than 0.35 percent by volume of water.
Various systems have been devised for monitoring the moisture content of the oil and for producing an alarm signal when the moisture content exceeds an unsafe level. Many systems which have been used commercially, however, are unreliable and experience a relatively short service life. In many instances, such systems malfunction and fail to produce an alarm signal to warn the operating personnel that the water content has risen to a dangerous level. One of the possible causes resulting in a malfunction is that the sensing element for detecting the water becomes fouled by the oil and loses its sensitivity. Also, various additives and contaminants in the oil may cause the sensing element to produce a false signal or no signal at all. In some instances, the high temperature of the oil bath causes the sensing element to deteriorate. In still other instances, the sensing element must be re-conditioned for re-use once the element has been exposed to a high moisture content.